Referring to FIGS. 1A and 1B, in this type of printer, when a printed sheet (roll paper) S is being discharged in a discharging direction F, if an obstacle such as a user's hand is placed in front of a discharge port 13 to interrupt the discharge of the sheet S, as illustrated in FIG. 1B, the sheet S may be rolled around a conveyance roller 14 for conveying the sheet in an inner part of the printer, that is, in a sheet conveyance path between a lower frame 11 and an upper frame 12, with the result that paper jam may occur.
As a countermeasure for preventing the paper jam, a sheet discharge device configured as illustrated in FIG. 1C is known. Referring to FIG. 1C, in this printer, a retreat region for the sheet S is formed so as to communicate to the sheet conveyance path, and a deflection sensor 16 for detecting the sheet S that has deflected to enter the retreat region is provided. Based on a detection signal of the deflection sensor 16, the rotation of the conveyance roller 14 is controlled and stopped, to thereby urgently stop the discharge operation of the sheet S. After that, the obstacle in front of the discharge port 13 is removed, and the printer is operated again.
By the way, the paper jam occurs also when the discharging direction of the sheet (the same direction as the conveyance direction) has deviated in a paper width direction, as well as when the discharge of the sheet has been hindered by an obstacle as described above. For example, in a printer illustrated in FIGS. 2A to 2C, when the sheet S is being discharged as illustrated in FIG. 2B (at a stage where a trailing edge of the sheet S in the discharging direction is in contact with the conveyance roller), if the sheet S is pulled by a user as illustrated in FIG. 2C to deviate in a paper width direction W orthogonal to the discharging direction F (this state is referred to also as being subjected to transverse tension) and if the conveyance roller continues rotating under the state where the sheet S deviates in the paper width direction W, the sheet S is rolled around the conveyance roller to cause paper jam.
Note that, when the sheet is subjected to the transverse tension, unlike when an obstacle is present in front of the discharge port, no deflection or only a little deflection occurs in the sheet in the sheet conveyance path. The conveyance of the sheet S is therefore not stopped even by the configuration illustrated in FIG. 1C using the deflection sensor, and paper jam occurs as illustrated in FIG. 1D. In other words, the configuration illustrated in FIG. 1C cannot reliably prevent the paper jam caused by the transverse tension of the sheet.
As a countermeasure for preventing the paper jam caused by the transverse tension of the sheet, there is known a technology in which guide means for restricting the deviation of the sheet in the paper width direction are provided in the vicinity of the discharge port for the sheet. For example, in the printer illustrated in FIGS. 2A to 2C, as illustrated in FIG. 2A, a pair of guide pieces 68 is formed to have an interval therebetween corresponding to a width dimension of the sheet S when the sheet S is discharged in a normal discharging direction F.
The printer including this type of guide means is, in addition to the one illustrated in FIGS. 2A to 2C, also disclosed in, for example, Related Art Document 1 (Japanese Unexamined Patent Application Publication (JP-A) No. Sho 59-155082) and Related Art Document 2 (Japanese Unexamined Patent Application Publication (JP-A) No. Hei 11-208048). It is found in the technology disclosed in Related Art Document 1 that a guide hole formed in a member called a guide has an opening dimension corresponding to a width dimension of the sheet and hence the sheet can be restricted from deviating in the paper width direction to some extent. It is also found in the technology disclosed in Related Art Document 2 that a guide wall formed on a guide member has an opposing dimension corresponding to a width dimension of roll paper and hence the roll paper can be restricted from deviating in the paper width direction to some extent.
However, the guide means in the example illustrated in FIGS. 2A to 2C and the examples disclosed in Related Art Documents 1 and 2 allow the sheet to deviate in the paper width direction because, when the sheet is subjected to transverse tension, the sheet deflects in the paper width direction as illustrated in FIG. 2C. In other words, in the example illustrated in FIGS. 2A to 2C and the examples disclosed in Related Art Documents 1 and 2, the paper jam caused by the transverse tension of the sheet cannot be prevented reliably.